61925-85-7Relevant articles and documents
Steric effect of NHC ligands in Pd(II)–NHC-catalyzed non-directed C–H acetoxylation of simple arenes
Mandal, Tanmoy,Yadav, Sudha,Choudhury, Joyanta
, (2021/09/06)
Although there has been a lot of progress in oxidative arene C–H functionalization reactions catalyzed by Pd(II/IV) system, the non-directed, site-selective functionalization of arene molecules is still challenging. It has been established that ligands play a pivotal role in controlling rate- as well as selectivity-determining step in a catalytic cycle involving well-defined metal-ligand bonding. N-heterocyclic carbene (NHC) ligands have had a tremendous contribution in the recent extraordinary success of achieving high reactivity and excellent selectivity in many catalytic processes including cross-coupling and olefin-metathesis reactions. However, the immense potential of these NHC ligands in improving site-selectivity of non-directed catalytic C–H functionalization reactions of simple arenes is yet to be realized, where overriding the electronic bias on deciding selectivity is a burdensome task. The presented work demonstrated an initiative step in this regard. Herein, a series of well-defined discrete [Pd(NHCR′R)(py)I2] complexes with systematically varied degree of spatial congestion at the Pd centre, exerted through the R and R’ substituents on the NHC ligand, were explored in controlling the activity as well as the site-selectivity of non-directed acetoxylation of representative monosubstituted and disubstituted simple arenes (such as toluene, iodobenzene and bromobenzene, naphthalene and 1,2-dichlorobenzene). The resulting best yields were found to be 75% for toluene and 65% for bromobenzene with [Pd(NHCMePh)(py)I2], 75% for iodobenzene and 79% for naphthalene with [Pd(NHCMeMe)(py)I2], and 41% for 1,2-dichlorobenzene with [Pd(NHCCyCy)(py)I2]. Most importantly, with increasing the bulkiness of the NHC ligand in the complexes, the selectivity of the distal C-acetoxylated products in comparison to the proximal ones, was enhanced to a great extent in all cases. Considering the vast library of NHC ligands, this study underscores the future opportunity to develop more strategies to improve the activity and the crucial site-selectivity of C–H functionalization reactions in simple as well as complex organic molecules.
Ligand-Promoted Palladium-Catalyzed C?H Acetoxylation of Simple Arenes
Valderas, Carolina,Naksomboon, Kananat,Fernández-Ibá?ez, M. ángeles
, p. 3213 - 3217 (2016/10/24)
The palladium-catalyzed C?H oxidation of simple arenes is an attractive strategy to obtain phenols, which have many applications in the fine chemicals industry. Although some advances have been made in this research area, low reactivity and selectivity are, in general, observed. This report describes a new catalytic system for the efficient C?H acetoxylation of simple arenes based on Pd(OAc)2 and a pyridinecarboxylic acid ligand.
Steric control of site selectivity in the Pd-catalyzed C-H acetoxylation of simple arenes
Cook, Amanda K.,Emmert, Marion H.,Sanford, Melanie S.
supporting information, p. 5428 - 5431 (2013/11/19)
This report describes the use of an oxidant and a ligand to control site selectivity in the Pd(OAc)2-catalyzed C-H acetoxylation of simple arenes. The use of MesI(OAc)2 as the terminal oxidant in combination with acridine as the ligand results in primarily sterically controlled selectivity. In contrast, with Pd(OAc)2 as the catalyst and PhI(OAc)2 as the oxidant, electronic effects dominate the selectivity of arene C-H acetoxylation.
Remarkably high reactivity of Pd(OAc)2/pyridine catalysts: Nondirected C-H oxygenation of arenes
Emmert, Marion H.,Cook, Amanda K.,Xie, Yushu J.,Sanford, Melanie S.
supporting information; experimental part, p. 9409 - 9412 (2011/11/07)
Less is more: The rational optimization and general applicability of the catalytic system Pd(OAc)2/pyridine is described (see scheme). The catalyst shows excellent reactivity in the C-H oxygenation of simple aromatic substrates. The Pd/pyridine ratio is critical as the use of one equivalent of pyridine per Pd center leads to dramatic enhancements in both reactivity and site selectivity in comparison to Pd(OAc)2 alone.
Platinum and palladium complexes containing cationic ligands as catalysts for arene H/D exchange and oxidation
Emmert, Marion H.,Gary, J. Brannon,Villalobos, Janette M.,Sanford, Melanie S.
supporting information; experimental part, p. 5884 - 5886 (2010/11/19)
Cationic catalysts in HD: Palladium(II) and platinum(II) complexes of pyridinium-substituted bipyridine ligands are highly active and stable catalysts for H/D exchange and oxidation of aromatic C-H bonds (TONs up to 3200, TOFs up to 0.1 s-1; se
Highly efficient dynamic kinetic resolution of secondary aromatic alcohols with low-cost and easily available acid resins as racemization catalysts
Cheng, Yongmei,Xu, Gang,Wu, Jianping,Zhang, Chensheng,Yang, Lirong
supporting information; experimental part, p. 2366 - 2369 (2010/06/13)
A new and efficient dynamic kinetic resolution (DKR) process of secondary aromatic alcohols was developed with acid resins as racemization catalysts. Acid resin CD8604 was shown to have excellent racemization activity and good biocompatibility. When employing CD8604 and complex acyl donors as racemization catalyst and acyl donor, respectively, enantiomerically pure aromatic acetate was obtained with excellent yield and ee values through the DKR process. It is noteworthy that the system could be reused more than 10 times with little loss of yield and ee value.
Retention behavior of compounds with active hydrogen atoms and their acetylated derivatives in reversed-phase HPLC
Zenkevich,Kosman
, p. 1173 - 1176 (2007/10/03)
In view of poor interlaboratory reproducibility of retention indices I in reversed-phase high-performance liquid chromatography, not the indices themselves but their differences for reactants and products of interaction with various reagents can be used to identify compounds with active hydrogen atoms. For acetylated derivatives of phenols and aromatic amines, the quantity ?I = I(ArXH) -I(ArXCOCH3), where X = O or NH. has statistically significant distinguishable values of 126 ± 15 and 70 ± 20, respectively. The additivity of the parameters ?I is first revealed for the polyfunctional compounds of these classes that are incapable of intramolecular hydrogen bonding. Abnormal ?I values and deviations from the additivity rule are observed only for substances with intramolecular hydrogen bonding. This finding can be used to confirm the presence of relevant structural units in molecules.
Structure-reactivity correlations for reactions of substituted phenolate anions with acetate and formate esters
Stefanidis, Dimitrios,Cho, Sayeon,Dhe-Paganon, Sirano,Jencks, William P.
, p. 1650 - 1656 (2007/10/02)
The reactions of substituted phenolate anions with m-nitrophenyl, p-nitrophenyl, and 3,4-dinitrophenyl formates follow nonlinear Br?nsted-type correlations that might be taken as evidence for a change in the rate-limiting step of a reaction that proceeds through a tetrahedral addition intermediate. However, the correlation actually represents two different Br?nsted lines that are defined by meta- and para-substituted phenolate anions and by meta- and para-substituted o-chlorophenolate anions. A concerted mechanism for both acetyl- and formyl-transfer reactions is supported by the absence of a detectable change in the Br?nsted slope at ΔpK = 0 for the attacking and leaving phenolate anions within each class of Br?nsted correlations. Regular increases in the dependence of log k on the pKa of the nucleophile with increasing pKa of the leaving group correspond to a positive interaction coefficient pxy = ?β1g/?(pKnuc) = ?βnuc/?(pK1g). The observation of two different Br?nsted lines for the reactions of substituted phenolate anions with phenyl acetates is attributed to a steric effect that decreases the rate of reaction of substituted o-chlorophenolate anions by 25-50%. The reactions of meta- and para-substituted phenolate and o-chlorophenolate anions with substituted phenyl acetate esters follow values of βnuc = 0.53-0.66 and -β1g = 0.50-0.63. The reactions of meta- and para-substituted phenolate anions with formate esters are ～ 103 times faster and follow smaller values of βnuc = 0.43-0.64 and -β1g = 0.31-0.48. However, the reactions of meta- and para-substituted o-chlorophenolate anions with the same formate esters follow larger values of βnuc = 0.63-0.90 and -β1g = 0.46-0.90. The large values of βnuc and -β1g for the reactions of substituted o-chlorophenolate anions with formate esters may arise from destabilization by the o-chloro group of a stacking interaction that is present in the transition state for reactions of formate esters, but not acetate esters.
Reductive Dechlorination of Chloro-phenols and -benzoic acids by Raney Co-Al Alloy in an Alkaline Deuterium Oxide Solution and Preparation of Deuterated Salicylic Acids
Tashiro, Masashi,Tsuzuki, Hirohisa,Matsumoto, Jun-ichi,Mataka, Shuntaro,Nakayama, Kouji,et al.
, p. 2826 - 2851 (2007/10/02)
Reduction of monochloro-phenols (1a-c) and -benzoic acids (3a-c) by using Raney Co-Al alloy in 10percent NaOD-D2O gave phenols (2a-c) and benzoic acids (4a-c) in 86-93percent isotopic purities.The reduction of di-, tri-, and tetra-chlorinated derivatives, (1) and (3), gave the deuteriated products, (2) and (4), in somewhat low isotopic purities (70-84percent).In the reduction of polychlorinated benzoic acids (3), the use of a mixed solution (1/1 = v/v) of 10percent Na2CO3-D2O and 10percent NaOD-D2O was effective and gave 4 in 80-89percent isotopic purities.The treatment of chlorosalicylic acids (5) with Raney Co-Al alloy in 10percent NaOD-D2O gave 1> (6) - 3> (6) in 91-93percent isotopic purities.
Concertedness in Acyl Group Transfer in Solution: A Single Transition State in Acetyl Group Transfer between Phenolate Ion Nucleophiles
Ba-Saif, Salem,Luthra, Ajay K.,Williams, Andrew
, p. 6362 - 6368 (2007/10/02)
Rate constants have been measured for nucleophilic substitution of 4-nitrophenol from 4-nitrophenyl acetate by a series of phenolate anions.The Bronsted type plot is linear for unhindered phenolate ions with pKa values significantly above and below that of the displaced 4-nitrophenol: (log kArO = 0.75pKArOH - 7.28; n = 17, r = 0.984); this is consistent with a mechanism involving a single transition state or a mechanism with an intermediate that has a very low barrier to decomposition.A small change in effective charge on the carbonyl group from reactant to transition state (measured from βnuc and the known βeq for the overall reaction) points to an almost coupled concerted mechanism for the transfer of acetyl function between phenolate ion nucleophiles.The conclusions of this work are consistent with previous results that indicate relatively stable tetrahedral intermedates in reactions at reactive acyl centers; a spectrum of mechanisms exists for substitution reactions of acyl functions in solution that ranges from SN1 (or ElcB for an ester with an α-carbanion) through concerted to BAc2.
